We provide, as a service, a method for cycle synchronization and prolonged luteal phase as required by other investigators. These investigators require that a group of female rhesus monkeys be in the mid-luteal phase of a normal menstrual cycle, all on the same day, so that the same virus inoculums could be used for vaginal inoculation. This synchronization is provided as follows The monkeys are observed daily for indications of menses. When it occurs, each monkey is then injected with progesterone starting on day 16 of that cycle. When all study monkeys have received at least 8 days of progesterone the injections are stopped. Menses occurs 2-3 days of the last progesterone injection. On day 16 of that cycle the monkeys began a second series of progesterone injections. The inoculations are done on a single day during this last series of progesterone. This procedure has provided study groups of 10 or more monkeys, all synchronized + 1 day in their cycle stage and maintained in a luteal stage for up to 21